Weather Modders Aim to End Droughts With Efficiency by Sky

Armed with new tech, cloud seeders fly to the rescue of water-starved regions of the country.

From the cockpit of a Cessna 340 A 10,000 ft. over North Dakota, I watch a bucolic conveyor belt of farming towns scroll below. Then, the whole world goes grayish-white.

"We're just popping through the edge of this cloud bank," says Hans Ahlness, a pilot and vice president of the Fargo-based company Weather Modification, which specializes in teasing rain from the sky. Ahlness points to a mushroom formation a few hundred feet away. "See how that cloud's got a cap on top? That means it's growing fast. That's what we're looking for." As we approach the gray cluster, the plane bounces up and down, like an elevator car on a slack cable. I swallow, fervently willing my breakfast to stay in my stomach. "We're getting a little bit of an updraft from the cloud," Ahlness says calmly, pointing to the altitude gauge on the instrument panel. "See how we're maintaining speed and still climbing?"

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One of the cardinal skills taught in flight training is how to steer clear of burgeoning storms, which toss two-seater planes around like balsa wood gliders and test the mettle of even experienced pilots. But Ahlness and his fellow cloud seeders fly directly into the roiling depths, firing dozens of foot-long flares that disperse a cocktail of salty substances as they burn up. The salt forms millions of ice nuclei that attract droplets of water. Eventually, the drops grow heavy enough to fall out of the sky as rain. "Our mission is to make inefficient clouds more efficient with aerosols that are lacking in nature," says Bruce Boe, Weather Modification's director of meteorology.

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Humans have been trying to change the weather since the earliest rain dances; showers produced by the first modern rainmaking experiments in the 1940s and '50s seemed more symbolic than practical. But the prospect of conjuring precipitation from stingy clouds has lost its mad-scientist overtones in recent years. Nearly half of the contiguous United States experienced drought in 2007, and scientists predict that water shortages will worsen with global warming. For many regions, engineering the weather is now viewed as an absolute necessity.

State and county governments have begun to fund weather-mod gurus with increasing urgency: The Wyoming Water Development Commission allocated $9 million for a five-year cloud-seeding research program. Similar efforts are underway in North Dakota, California, Utah, Colorado and Texas. Even Congress has gotten in on the act: Last year, Texas senator Kay Bailey Hutchison introduced a bill to establish a national weather mitigation policy.

"I'm just going to pass through this little cloud right here," Ahlness calls out, grinning. "Hang on!" The Cessna sweeps and dips like an agitated bird. Beneath the plane's wings are instruments that count precipitation droplets, sample aerosols, sense wind flow and measure the liquid content of clouds. While flares haven't changed much since the 1960s--salt-based silver iodide is still the seeding agent of choice for most firms--the addition of remote sensing instrumentation is relatively new, and increasingly common. Fed into sophisticated weather-simulation models, this data gives scientists a much more detailed portrait of cloud conditions--including factors like the size and temperature of existing droplets, the presence or absence of ice crystals and the concentrations of pollutants--and predicts how successful a particular type of seeding will be. Silver iodide, for instance, works best on supercooled clouds made of water droplets colder than 23 F.

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"It used to be that pilots would just take off and find the strongest updraft to decide where to seed," says Darin Langerud, director of North Dakota's Atmospheric Resource Board. "Now researchers are able to tell you things like, 'You don't want to seed the main updraft, you want to seed another updraft on the flank of the cloud formation.'"

Still, despite high-tech refinements, some scientists remain unsure whether the modifiers' strategies are any more effective than burnt offerings to the rain gods. This skepticism dates back decades: Federal funding for cloud-seeding programs dwindled to almost zero in the 1990s, when studies that gauged the effectiveness of different rainmaking strategies yielded mixed findings.

Current research indicates that, on average, cloud-seeding measures boost precipitation in North Dakota by 4 to 10 percent annually--and up to 20 percent across the nation--but because weather conditions vary so much from year to year, seeding programs don't often obtain consistent results. A 2003 National Academy of Sciences report concludes: "There is ample evidence that seeding a cloud with a chemical agent can modify the cloud's development and precipitation. However, scientists are still unable to confirm that these induced changes result in verifiable, repeatable changes in rainfall." When Bill Cotton, an atmospheric scientist at Colorado State University, developed a computer model to evaluate seeding measures in Colorado, he came up empty. "The model didn't show much of a difference between seeding and no seeding," he says.

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Most cloud seeders have a healthy understanding of the limitations of their trade. "A 4 to 10 percent increase in rainfall isn't a tremendous amount," Langerud says, "but it could translate into an inch of additional rain during growing season." North Dakota counties that have signed on for seeding enjoy roughly $8 million in increased agricultural production each year, with an annual investment of about $700,000. These returns, according to Langerud, make seeding a more attractive drought-busting measure for cash-strapped states than traditional fixes such as building new dams and reservoirs. "It's like, 'I'll give you a dollar, you give me 10 back,'" he says. "That seems like a pretty good deal to me."

On this particular August day, our mission into the upper troposphere seems doomed. In the old days, pilots like Ahlness would have gone with their gut instincts. But modeling data from the ground crew indicates these clouds aren't big or droplet-packed enough to make firing flares worthwhile. "Every system is different," Ahlness says as we head back toward the ground. Despite the false starts and the ongoing debate over cloud seeding's merits, Ahlness and his fellow pilots remain true believers, willing to devote their careers--and even their free time--to the cause. Like emergency room doctors, Weather Modification's wingmen must keep their pagers on 24/7 in case they're called on for middle-of-the-night missions. They love to grouse about the inconvenience, but it's obvious they live for the rush. "Look--there's a cell over there that's just getting going," Ahlness says with a kid's unfettered excitement. As soon as the burgeoning fronts around us converge into another perfect storm, he'll take to the skies again.